A number of techniques have been used over the years to join individual sheets of roofing materials. As will be appreciated by those skilled in the art, rubber membrane roofing materials are flat sheets of either single-ply or multiple-ply sheets formed of polymeric materials such as ethylene propylene diene monomer or isoprene isobutylene copolymer. These sheets are typically provided in large rolls of material of standard widths. After a section of sheeting material is applied to a roof surface, a second section is laid down partially overlapping the first section. This overlap is critical to ensure that a gap is not created between the sheets which would allow water to penetrate the roof surface.
In order to create a water-tight seal between the adjacent, overlapping roofing sheets, it is necessary to create a water-impervious bond at the splice or lap-joint. This is generally achieved by interposing an adhesive between the two roofing sheets at the region of overlap. The surfaces to be bonded together may be cleaned prior to application of the adhesive using a solvent or the like to enhance the bonding process and a primer may be applied to the cleaned surfaces to further increase the bond strength of the adhesive.
In some applications a liquid contact adhesive has been applied to one or more of the roofing sheets at the lap-joint which is then allowed to dry. The sheets are then overlapped and pressure is applied to cause the contact adhesive to bond the two sheets together. After the two sheets are joined in this manner, a caulking material may be used along the edge of the top layer at the joint and/or internal to the lap-joint (ref U.S. Pat. No. 4,849,268) in order to provide additional protection against water intrusion.
Another technique for joining two sheets of roofing material involves the use of adhesive roofing tapes. These tapes are designed to take the place of liquid roofing adhesives. Conventional tapes are provided as a roll having a release liner. The tape is separated from the backing material and is applied to the surface of the roofing sheet at the region where the lap-joint is to be formed. It will be understood that the tape is interposed between the overlapping surfaces of the roofing sheets along the entire length of the joint.
There are a number of important requirements for quality adhesive roofing tapes. Most importantly, they must provide a good water-tight bond at the lap-joint. In addition, they must resist environmental degradation for many years; a premature failure of the tape may result in extensive water damage. It is important that the tape retain some flexibility so that the lap-joint does not fail as a result of thermal expansion and contraction of the roofing sheets.
A number of prior art roofing tapes have been proposed. One type is an uncured strip of elastomeric material which is interposed between the roofing sheets and which cures thereafter by exposure to normal solar heat. Another type remains uncured throughout its service life. A third type of roofing tape is partially or substantially fully cured in the factory prior to its application to the roof.
Several examples of roofing tapes appear in the prior art patent literature. In U.S. Pat. No. 4,588,637 entitled, "Adhesive Composition" there is disclosed a membrane adhesive tape comprising a layer of butyl rubber-based material formed by compounding a minor portion of a butyl rubber copolymer, a curing agent for the butyl rubber, carbon black, and a major portion of a tackifier which forms a surface tack on the tape. The tape is pre-cured prior to use.
In U.S. Pat. No. 5,242,727 entitled, "Adhesive Composition and Method for Providing Water-Tight Joints in Single-Ply Roofing Membranes" a roofing membrane adhesive tape is disclosed comprising substantially equal amounts by weight of (1) a rubbery polymer comprising a blend of an ethylene-propylene-diene terpolymer, a halogenated butyl rubber or a halogenated co-polymer of p-methylstyrene and isobutylene, and polyisobutylene and (2) a compatible tackifier. The composition is fully vulcanized prior to use.
Additional such compositions are shown in U.S. Pat. No. 4,742,119 entitled, "Protective and Adhesive Compositions"; U.S. Pat. No. 4,881,996, "entitled, Splice Adhesive for EPDM Roofing and Splicing Method Employing Same"; and U.S. Pat. No. 4,601,935 entitled, "EPDM Laminate."
A number of difficulties have been encountered with commercially available roofing tapes. Roof curing type tapes have shown heat related creep failure tendencies prior to full cure and tend to cure to an unusable state during storage. Uncured tapes suffer from poor heat resistance plus the above mentioned creep failure problems. As a group, only the factory cured tapes have shown reliable performance. However, many of these tapes suffer from bleeding of tackifier into the vulcanized membrane, resulting in the accumulation of dirt and staining of the membranes at the splice, leaving a porous tape film. In addition many commercial tapes often have reduced tack at temperature extremes. Some have poor resistance to UV light.
Problems have also been encountered with splitting and tearing of the release paper as it is removed from the tape in the field. Also, the tape often "jumps" across the roll between opposed paper surfaces as it is unrolled. It is believed that these latter problems are due to the inability to maintain consistency in the processing techniques.
Accordingly it is an object of the present invention to provide an adhesive for joining together two roofing membranes which substantially reduces the bleeding of liquid components into the membranes.
It is another object of the present invention to provide such an adhesive in the form of a high-tack roofing tape which has good processing characteristics and which has high UV light resistance.
It is still another object of the present invention to provide an adhesive roofing tape having high temperature creep resistance, good tensile strength and good elongation characteristics.